A robot of the kind defined by way of introduction is described in U.S. Pat. No. 4,976,582. For the positioning of the second element, the robot comprises three force-applying arrangements, which in unison comprise three force-exerting members arranged in a triangular distribution on the first element. Each of the force members is connected to the movable second element via its own connection comprising two link arrangements and an intermediate connection arrangement. These three connections coupled in parallel are likewise arranged in a triangular configuration. Each of these connections comprises a first link arrangement including two first links pivotably connected to the second element and a second link, which is rigidly connected to a movable portion of the force-exerting member and by means of a connection arrangement is connected to the two first links. The second link is movable with regard to one single degree of freedom relative to the stationary portion of the power-exerting member. The connection arrangement connects the first and second links in a hinged manner with no more than two degrees of freedom. The link arrangement formed by the first links is connected to the second element so that two but not more than two degrees of freedom occur. The first link arrangements form parallelogram-shaped four-links systems. A disadvantage with this known type of robot is that it becomes comparatively bulky as a consequence of the triangular configuration discussed herein above. The angle between planes of pivoting of two adjacent second links must, always be less than 180.degree.. Thus, it is very difficult to arrange two or more of those robots closely to each other without collision. A further disadvantage is that it is structurally difficult to design the known robot with the required stiffness and strength since the movable portions of the three power-exerting members project in a star-like fashion from the first element, which regarding the space requirement should be formed as small as possible but on the other hand must be able to receive the power-exerting members. Thus, it becomes difficult to design arms rigidly connected to the movable portions of the power-exerting members with a sufficient width as far as the arms themselves are concerned as well as their bearings at the first element.
A further disadvantage is that all arm lengths must be equal. This means that it is not possible to optimize the robot to the pattern of movement in question. Performance will always be symmetrically distributed in a symmetrical working area, which is not cost efficient.
Also, the known robot cannot execute a tilt movement of the second element to fetch objects located sidewardly of or above the robot.
In addition, three further motors are required in order to change the inclination of the second element. It would be desirable to manage this with only one extra motor in order to achieve a cost-efficiently.
As a consequence of the equilateral triangular construction of the known robot it is also difficult for arrange to work horizontally above conveyors, loading pallets etc. Furthermore, if a working member on the second element is to be driven by means of a motor on the first element, an axle extending between the first and second elements must comprise a torque-transmitting coupling allowing variation of the length of the axle. In practice, the axle is suitably designed as consisting of two axle parts, which are displaceable telescopically relative to each other and the torque transmission of which is ensured by splines, wedge grooves or similar. This complicates the embodiment and makes it more costly.